1. Field of the Invention
This invention relates to a vacuum excavation system for safely dislodging and removing soil from around buried objects without damage using a combination of supersonic jets of air and pneumatic vacuum transport.
2. Description of the Prior Art
There is a significant need for an improved system that is capable of performing excavation in a safe and efficient manner for civilian, industrial, and military applications. Existing buried gas, electric, water, telephone and sewer utility lines are in constant need of repair and replacement. Though buried utility line detection technologies continually improve, lack of accurate location records and other practical problems lead each year to millions of dollars of expense and even explosions and loss of life due to excavation accidents involving underground lines. New service lines, such as cable television, must be added into areas with other existing utilities. New technologies such as ground-based, heat pump storage systems require large lengths of lines to be installed adjacent to existing homes and businesses. In the area of environmental remediation, drums, boxes and other containers of environmental waste buried in the past now need to be either removed or re-encapsulated due to leakage or more stringent standards. Finally, in the military sector there are millions of acres in the United States that contain buried unexploded ordnance that must now be removed to reclaim those acres for civilian purposes.
Several variations of vacuum excavation systems or vacuum assisted mechanical excavation systems are known in the prior art. U.S. Pat. No. 5,016,717 discloses an excavation system having a truck mounted suction tank connected to a vacuum blower. A hand-held wand with a liquid jet is provided to dislodge the soil and a hand-held flexible hose connected to the tank is provided to suck up the material.
German Patent No. DE 4138619-A describes a vehicle on wheels with a boom mounted cyclone type separator with a soil suction tube for excavating unmapped underground service lines. The soil suction tube hangs vertically from a flexible elbow and a rigid tube, which is in turn hydraulically raised and lowered. The suction tube has a curved inlet. A "Luftlanze" (air lance) alongside of the soil suction tube loosens the soil. The separator is round with a tangential material entrance and a bottom dump door.
Japanese Reference No. JP 58-222223 shows a rubber tired vehicle with a corrugated vacuum hose to suck up material from an excavation. The hose has several bends in it and includes a rigid end with a slight venturi on the open end. The hose disgorges its material into a primary box where the air travels through a permeable membrane and the material falls down to the bottom of the box under gravity and the reduced air velocity. The air travels into a second box where there are bag type filters. Slide gates are used to empty material from the boxes. Clean or filtered air that passes through the bags is drawn in by a rotary lobe type of blower which discharges into the atmosphere via a silencer. The blower is driven by an internal combustion engine.
U.S. Pat. No. 5,120,165 discloses a general pneumatic excavation system using a special multi-stage cyclone separator. This patent also discloses the use of a soil fragmenting device that includes mechanical, explosive and/or hydraulics.
U.S. Pat. No. 3,930,324 discloses a mobile, mechanical digging machine comprising a rotary cutting tool around a central suction tube. This digging machine is intended for small hole, utility type excavations for maintenance and repair. The rotary cutting tool is mounted to be moved in both horizontal and vertical directions and is deliberately powered sufficiently to be able to cut through macadam or asphalt. (Protection against cutting utility pipes is provided by an electromagnetic metal detector; hence, plastic pipe, i.e., modern gas pipe, is undetected.)
U.S. Pat. No. 3,968,845 discloses a truck mounted apparatus and method for complete reverse air geological drilling and coring. A conventional mechanical drill string is used to drill a vertical hole in the earth. Core material collection is accomplished by atmospheric air pulled first down through an annulus defined between the drill string and a bore hole wall and then passed up through the inside of the drill string at high velocity by an onboard vacuum pump. Conventional cyclones, hoppers and bags are used to separate the material from the airstream.
Finally, U.S. Pat. No. 4,434,861 discloses a method and apparatus for pneumatically conveying and collecting drill cuttings from a mechanical drill hole. This patent discloses an arrangement that surrounds the drill string and an arrangement for removing the material from the air via a combination of inertia, gravity, or filters.
Several patents disclose specific heads that use a combination of air and vacuum for general material dislodging purposes. For example, U.S. Pat. No. 4,936,031 describes a soft excavator using a rotary digging head with multiple supersonic air jets and a central vacuum. Compressed air is supplied to the rotating head via an annular chamber. The jets trace out an epitrochoidal pattern around the vacuum inlet. The head is mounted on a rigid vertical boom that is driven up and down via a rack and pinion gear arrangement. U.S. Pat. No. 4,995,175 discloses a pneumatic excavation head for underwater debris. Compressed air is introduced down an annulus and out through multiple openings into the sand and gravel bottom to loosen and lift it into a central pipe. U.S. Pat. No. 3,916,634 describes a method to form vertical holes in the earth using air of at least seventy-five psig released uniformly from an annulus to loosen and lift material into a central pipe. U.S. Pat. No. 3,395,467 discloses a head for harvesting peat moss that uses a first airstream to loosen a top strata of dryer, milled material from a bottom strata of damper material and a second airstream to entrain and transport the loosened dryer material. U.S. Pat. No. 3,678,534 describes a vacuum cleaner head with a suction tube and multiple small diameter orifices fed by gas at a pressure on the order of forty psig, such that gas jets exit these orifices at supersonic speed and impinge on a surface to be cleaned.
Commercially available vacuum excavation units today have common features and common problems with soil dislodging and transport. Aside from the mechanical diggers mentioned above, which are certainly not non-damaging to buried objects, the units use a fluid under pressure released from a hand-held lance to dislodge the soil. Some units use water released under moderate pressure. Water has a number of disadvantages including: making mud which is difficult and disagreeable to handle; adding weight and volume to the waste stream which needs to be disposed of; freezing in the excavation in the winter; and needing to be carried onboard the unit taking up significant space and adding weight that must be transported. Most units use air as the working fluid released simply through the open end of a pipe nipple with air flows from seventy-five to one hundred and eighty-five standard cubic feet per minute (scfm) at generally one hundred pounds per square inch gauge (psig). Although an air lance, including a valve and a pipe is rugged and cheap to make, it results in an inefficient compressed air digging tool. Compressed air exiting from the open end of a pipe nipple in an air lance expands suddenly to atmosphere in a broadened manner with a loss of focus of kinetic energy and momentum. For example, considering a standard portable air compressor of one hundred seventy-five scfm at one hundred psig, the wasted fuel costs for an air lance over a properly designed supersonic air jet is about fifty dollars for every one hundred hours of use. Viewed another way, to do a given amount of work, the size of the compressor needed is also larger than necessary due to the inefficiency of an air lance.
All of the current commercial vacuum excavation units use simply a vacuum hose to convey the material from the excavation to the hopper. Two types of hoses are commonly used: an inexpensive corrugated lightweight underground drainage type plastic hose, or a heavy wall rubber vacuum hose. The lightweight, inexpensive hose can be slung over a laborer's shoulder and is very flexible. However, this flexibility typically causes many severe bends in the hose. These bends lead to serious clogging problems and high suction losses. The frequent clogs are cleared either by wrapping the hose with a mallet or replacing the entire hose, both of which take time away from the digging. The other heavy rubber hose is too expensive to be discarded. Descended from sewer sucker types of trucks, typically the heavier hoses are used along with water jets. The water provides lubrication to allow the material to slide along the inside of the hose. Because of their high weight, this type of hose is supported from a fixed boom which is raised or lowered hydraulically, but moved by hand from side-to-side which can be difficult and fatiguing.
Typically, all of the vacuum excavation units also suck the soil into a hopper or tank. Tank sizes vary with about 70% of the units having a volume less than about forty cubic feet. In all cases, the tank size limits the amount of work that can be done before the process has to be interrupted. The larger the tank, the more space is taken up on the unit and the greater the cost of the tank since it must be designed to take the full vacuum capacity of the system. When the vacuum excavator tank is mounted on the truck and the spoil cannot be put back in the hole by local regulation, the truck itself needs to leave the work site when its tank is full.
Therefore, it is an object of the present invention to provide for an excavation system that overcomes the problems of the prior art.